La-Co-Ce-O复合氧化物催化剂的制备、结构与性能

Preparation,Structures and Properties of La-Co-Ce-O Complex Oxides

采用柠檬酸络合法制备出具有不同原子比(La+Co/La+Co+Ce)的La-Co-Ce-O系列复合氧化物,并采用XRD、XPS和H2-TPR等方法对样品进行了表征测试.XRD结果表明,样品中的活性相为高分散的Co3O4纳米微晶(20～50 nm)和少量的LaCoO3相,与浸渍法相比,柠檬酸络合法制得的样品具有更高的组分分散度和更小的晶粒度.CO氧化活性测试结果表明,柠檬酸络合法制得的样品比传统浸渍法制得的样品起燃温度降低约40℃,但样品的氧化活性与活性相Co3O4的多少及其晶粒度并不呈顺变关系.TPR和XPS的结果表明,样品中CeO2含量及可还原氧物种的多少与活性有直接关联,样品表面La、Co和Ce的原子百分数接近时,协同效应最佳,活性最好.

A series of La-Co-Ce-O complex oxides catalysts with various atomic （La ＋ Co/La ＋ Co ＋ Ce） ratios were prepared by citrate-complex method. The catalysts were characterized by means of XRD, H2-TPR and XPS techniques. Their catalytic activities for CO oxidation were measured in a fixed-bed reactor. The results of XRD reveal that the active phases are highly dispersed CO3O4 crystallinity （20～50 nm） and traces of LaCoO3. The sampies prepared by citrate-complex method possess higher component dispersion and much smaller crystal sizes than those prepared by conventional impregnation method, and therefore, the light-off temperatures （T50） of the former samples are decreased about 40℃. However, the oxidation activity is not totally depended on the content of Co3O4 and its crystal size. The results of TPR and XPS indicate that the content of CeO2 and the amount of surface reducible oxygen species in CeO2 are also relevant to the activity. When the surface atomic percentages of La, Co and Ce are close to each other, they show the best catalytic synergetic effect for CO oxidation.